The present invention generally relates to air bags used in an occupant protection safety system and more particularly to an air bag made from a single piece of material.
Conventional air bags are typically manufactured using several pieces of cloth that are cut in a prescribed pattern and sewn together to create an inflatable cushion having the desired shape. It is also known in the art that an air bag can be manufactured from a single piece of material. This type of air bag is shown in U.S. Pat. Nos. 5,316,337 and 5,310,216. As can be appreciated, the use of a single piece of material may lead to economies of manufacture.
Reference is made to FIG. 1 which illustrates an inflated air bag 20 which is made from a single piece of material which when laid flat is similar to the pattern shown in the above mentioned patents. This pattern of material (arranged as a single piece of material or using a plurality of pieces of material) typically includes geometric shapes having straight edges adjacent each other. When assembled, the air bag 20 will include a first, face or front portion 22, an inlet or neck 24 adapted in a known manner to be wrapped or fitted about an air bag manifold, which holds an inflator (or directly to an inflator), and a middle portion 26 interconnecting the front 22 and inlet 24 portions. Prior to inflation the cushion is folded or rolled into a compacted configuration and positioned about an inflator (not shown) and secured to a housing 25. The middle portion 26 is formed by joining various straight edges of the material pattern together at a plurality of seams 28a,b,c. As can be appreciated, FIG. 1 illustrates the right hand side of air bag 20. The left hand side of air bag 20 will also include a similar or identical pattern of seams. As can be appreciated, if the material pattern comprises a series of straight edges, the resulting seams will also be straight. The typical layout of the seams of this type of air bag 20 has a straight side seam such as 28a running from the inlet 24 toward the front portion 22 and radially diverging straight seams such as 28b and 28c. Experience has shown that the straight sides of the material pattern and resulting straight seams constrain design alternatives by limiting the number of shapes a cushion can have. In addition, such a cushion may require unwanted and unneeded folds and tucks to achieve its folded or compact configuration. This type of air bag also displays a less than optimal stress distribution, which overly stresses the material at the seams, which may result in leakage or tearing (at or near the seams) when the air bag inflates. This stress distribution results because the seams lie in a straight line along the contour of the inflated cushion and in line with the direction of air bag inflation. Upon activation of the inflator, inflation gas is produced or transmitted to the air bag which causes the air bag to unfold or unroll in a rapid manner, rapidly propelling the cushion material in a direction away from the housing 25 (generally toward the occupant to be protected, see arrow 27) at a high rate of speed. As the material reaches its maximum extension and decelerates, high stresses will be developed in the straight seams which tends to pull the seams apart especially at the common point such as 36 which often exhibits a region of maximum stress. During inflation the cushion 30 will generally become pressurized evenly throughout such that the top 32, bottom 34 and sides 35 of the cushion 30 will expand outwardly and the face or front portion 22 of the cushion material will pull away from the inlet (housing) stressing the seams. The momentum of the inflation gas particles generally acts to propel the bag toward the occupant in direction 27 while at the same time push the cushion generally in the direction of arrows 36 and 37. As can be appreciated, stresses are produced which are tangent or parallel to the seams (running along the exterior contour of the bag) which tends to pull the seams apart. In general, the seams represent a discontinuity in the cushion material, and therefore are the weakest part of the cushion.
In contrast, the present invention utilizes a one-piece, material pattern with a series of concave and convex edges that are joined together forming corresponding Princess seams or seam lines. As will be seen, this construction permits the cushion material, rather than the seams, to absorb the developed stresses. Further, the convex and concavely seams give the designer (of the air bag) the ability to achieve a greater number of bag shapes and to reposition the seams away from the regions of maximum stress such that the material, rather than the seams, absorbs the stresses. As such, the stresses generated are less prone to break the seams.
Accordingly the invention comprises: an inflatable air bag having: an inlet portion adapted to be attached to a source of inflation gas and a cushion portion, initially maintained in a folded or rolled configuration prior to being inflated, the cushion portion being rapidly inflated by the inflation gas wherein certain stresses are created within the material of the cushion during the inflation interval, the cushion including a plurality of convex/concave sets of seams joining certain edges of the cushion material together to thereby form the cushion, wherein the seams are arranged about the cushion at locations remote from the location of maximum stress.
It is an object of the present invention to provide a robust air bag and one that is easy to manufacture. The manufacturability of this cushion is improved by reducing the number of manual steps (such as the number of seams) and equipment (as an example quilting machines, may not be required), the number of parts, the amount of cloth required, and the amount of time to cut the cloth and sew the cushion. All of these improvements create a cushion that improves quality while reducing manufacturing costs.